This invention concerns machining of soft plastic foam material. Such material is commonly used for the care of automotive seats, which are manufactured by molding in a well known manner.
Automotive seats are often reconfigured for the various car models. The design process involves constructing prototypes for testing and evaluation. Since the tooling for molding the seat core is very costly, the prototypes are constructed by other methods. Hand sculpting of blocks of soft foam has typically been done in this industry, but this approach does have limitations as to accuracy and consistency and is slow and requires painstaking attention. It is getting more difficult to obtain the services of suitably skilled and careful craftsman.
Machining of the foam by suitably programmed CNC machine tools has also been practiced but this has also presented problems in achieving the required accuracy at a reasonable cost.
One difficulty is created by the easily compressible characteristic of the soft polyurethane foam used for seat cores and the nature of the seat shape. A large block of plastic is machined on one side to remove material to form one side of the seat shape. The block is reversed and the opposite contour machined into the reverse side of the block. It has been discovered by the present inventor that minute deflections of the foam material caused by the forces imposed by the cutting tool creates significant inaccuracies in the contour machined on the reverse side after the first contour has been machined due to the slight but significant reduction in stiffness occurring as a result of the removal of some of the foam material from the side first machined. That is, deflections of the foam material away from the cutting tool causes inaccuracies in the contour sought to be machined into the block.
It is an object of the present invention to provided a low cost but consistently accurate method of machining soft plastic foam material.
The above recited object and other objects which will be appreciated upon a reading of the following specification and claims are achieved by carrying out automated routing on low cost CNC router table using a burr type contouring tool to route one side of block of soft foam material having its sides clamped on the table by angles secured to the table top. Upon completing of the machining of one side of the block, the resulting cavity is packed with a granular filler material, advantageously the granular material produced by machining the block. The packed machined side is then covered with sheet plastic to confine the material in the cavity when it is turned over to expose the opposite unmachined side of the block.
Routing of the contour into the opposite side then takes place, with the packing yielding satisfactory accuracy due to the enhanced stiffness of the upward facing side of the block.